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ALEXANDER  TOJST  HTJaiBOLDT.                 179
the centre of the earth ; as, for example, Poisson, who
declares all heat to proceed from the exterior Inward;
but this hypothesis can now no more affect Hum-
boldt's theory, which if it were even only a supposition
fully explains many phenomena which would other-
wise be unintelligible.
An important mysterious force of the earth., which
surrounds all atoms of existence like a wonderful
chain, is magnetism, to which subject Humboldt has
devoted a great portion of his time. Every change of
temperature produces magnetic and electric streams,
and these Humboldt investigated for years by means
of the magnetic needle. The electro-magnetic streams
circulate mysteriously in a continual variety of deve-
lopment through the earth, and their changes, which
are shown by the sensitive needle, occur, to the hour,
according to place, solar position, and warmth, and
are suddenly modified only by the polar light. The
sudden interruption of the constantly-flowing earth-
magnetism, which takes place during the northern
light, occurs simultaneously, even if the observers
were thousands of miles distant; it is like a vibration
of the entire earth, or it runs like a pulsation in all
directions of the earth/s surface, with such extreme
regularity that distances might be measured by it.
Humboldt has not been able to ascertain the causes
of these sudden vibrations of the magnetic needle,
the sign of disturbances and revolutions in the earth's
magnetism.^ It is a known fact that all matter is
magnetic (-i. e. attractive) as long as it is pervaded by
electricity, and this fact may be explained by future
philosophers. Humboldt discovered the variability in
the mode of development,, the inclination and the
horizontal divergence of the earth-magnetism,, to be
the three phenomena by which this force can be
observed on the earth's surface. He added three
scientific lines as determining its equal force* equal
attraction, and equal repulsion, which he called the
* Hiiraboldt calls them magnetic storms.
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